These teachings relate generally to radio frequency (RF) receivers and, more specifically, relate to methods and apparatus for optimizing the performance of receivers such as those found in cellular telephones and other types of mobile communication devices and terminals.
The following abbreviations are herewith defined:
The power consumption of the third generation (3G) and multi-mode mobile phones is expected to increase as compared to present mobile communication systems. This is due at least in part to an expected increase in the required operational and the stand-by times. A need thus exists to even further reduce the power consumption of modem mobile phones.
A significant consumer of power in the mobile phone receiver is the VCO. The VCO is an important component that is used when automatically tuning in a high speed manner between different frequency channels. In conventional practice multi-mode operation is normally accommodated by the use of separate VCOs, one for each frequency band of interest. However, this approach obviously increases the cost and, in some cases, the power consumption. Another technique employs switched capacitor tuning. However, this approach does not necessarily provide a sufficiently wide frequency tuning range when state of the art performance is required.
The use of a tuneable current and/or rectifier in a VCO to tune the VCO core gain to achieve a more optimized performance, or to insure oscillation, is known in the art, as evidenced by A. Zanchi, A. Bonfanti, S. Levantino, C. Samori, and A. L. Lacaita: xe2x80x9cAutomatic Amplitude Control Loop for A 2-V, 2.5-GHz LC-tank VCOxe2x80x9d IEEE 2001.
However, further improvements and enhancements to dual mode VCOs are required in order to meet the stringent demands of modern mobile communications systems.
The foregoing and other problems are overcome, and other advantages are realized, in accordance with the presently preferred embodiments of these teachings.
In one aspect this invention provides for reducing the size and the current consumption of a dual frequency VCO circuit, where one core VCO is capable of operating in two different frequency bands with the aid of a transformer-connected serial resonance circuit. In a further aspect of this invention the VCO current is controlled by an amplitude/oscillation controlling circuit, where a rectifier/peak detector output signal may be used to determine whether the oscillator is operating or not. While the use of a VCO amplitude control loop may be generally known, the operation of an amplitude control loop when controlled by an algorithm of an adaptive receiver is not. If the requirement for the phase noise, defined by the received signal conditions, is less than a worst case value, the current consumption of the VCO can be reduced accordingly in an adaptive manner.
The VCO and its support circuits can be included on-chip along with other receiver components. The use of the on-chip design provides benefits in the form of accurate knowledge of loading and process variation effects. Because of this, an active buffer is replaced by passive buffering. The VCO buffer current consumption is typically 20%-30% of the VCO total power consumption. While the general idea of using a passive impedance transformation in order to isolate a VCO resonator from a load may be known, the use of passive impedance transformation in an on-chip implemented VCO is not. A benefit of this approach is a reduction in power consumption, as compared to an active buffer embodiment, such as one provided by a MOS source follower amplifier.
By the use of this invention the VCO current consumption can be reduced significantly. As was stated above, in conventional practice dual-mode operation is normally accommodated by the use of separate VCOs, one for each frequency band of interest. However, this approach obviously increases the cost and, in some cases, the power consumption. Another technique would employ switched capacitor tuning. However, approach does not provide a wide enough frequency tuning range when state of the art performance is required.
As was also stated above, it is known to use a tuneable current and/or rectifier in the VCO to tune the core gain. However, what is not known is a technique for adjusting the VCO to use it to reduce the current consumption, using information derived under different signal reception conditions.
A further benefit that is derived from the use of this invention is the realization of a sufficiently wide frequency separation between first and second operating bands (e.g., between WCDMA and GSM bands), while using only about one half of the chip area as compared to the use of two separate VCOs. In addition, a transformer impedance transformation reduces the effects of undesired components from the circuit that are added to the VCO to create the additional frequency band. It also provides a possibility to effectively detach these additional components while the VCO is operating an another frequency band. The use of the transformer thus reduces the effective loading of the resonator, and renders feasible a GSM/WCDMA on-chip VCO design. The transformer can also be used to connect other circuits to the VCO core without disturbing the operation of the VCO core significantly (i.e., a high degree of isolation is proved for the VCO core.)
While the Q of the transformer primary may be slightly less when the secondary is disposed beneath it in the chip layout, it is shown that by the use of a preferred layout, with careful design, the overall Q of the structure can be increased.
Disclosed herein is an RF VCO that forms, in the preferred embodiment, a part of a dual mode mobile station. Also disclosed is a method for operating the VCO. The VCO is operated in a first frequency band using a first inductance that forms part of a first resonant circuit (parallel resonance), and the VCO is switched for operation to a second frequency band by the closing a switch that causes a second resonant circuit (serial resonance) to be inductively coupled to the first resonant circuit. The second resonant circuit includes a second inductance, and preferably includes at least one frequency tunable component, such as a varactor, for adjusting the resonant frequency of the second resonant circuit. In the preferred embodiment of this invention both inductances are differential, and the switch, such as a MOS transistor or a MEMS component, is coupled in series between two ends of the center tapped secondary inductance.
As non-limiting examples, the first frequency band includes 3.6 GHz (a double frequency GSM band) and the second frequency band includes 4.3 GHz (a double frequency WCDMA band).
In the preferred embodiment the first inductance forms part of a transformer primary fabricated in an integrated circuit, and the second inductance forms part of the transformer secondary that is fabricated in the integrated circuit so as to underlie the first inductance.
Further in accordance with an aspect of this invention a signal detector is responsive to a signal induced in the transformer secondary, where the signal detector has an output coupled to a closed loop control circuit for controlling a magnitude of a signal output from the VCO. A further input to the closed loop control circuit may be a signal that is indicative of communication channel conditions, and the current consumption of the VCO circuit is maintained at a level that is adequate to ensure operation with the communication channel conditions.
An example of a system that can be used with this type of adaptive and dual band VCO is disclosed in commonly assigned U.S. Provisional Patent Application No.: 60/344,699, filed Dec. 28, 2001, entitled xe2x80x9cMethod and Apparatus for Scaling the Dynamic Range of a Receiver for Continuously Optimizing Performance versus Power Consumptionxe2x80x9d, by Aarno Pxc3xa4rssinen, Paul Seppinen, Jussi Vepsxc3xa4lxc3xa4inen, Mikael Gustafsson and Miika Hxc3xa4mxc3xa4lxc3xa4inen, the disclosure of which is incorporated by reference herein in its entirety.
Further in accordance with an aspect of this invention a passive buffering circuit is provided for coupling an output of the VCO circuit to a further circuit, such as a mixer or, as a further example, a divider.